Optical interconnection sheets for arranging a large number of optical fibers in two dimensions are disclosed, for example, in Japanese Patent No. 2574611 and Japanese Unexamined Patent Publication Nos. 2001-141936, 2001-147330, and 2002-174736. In any of these disclosed optical interconnection sheets, each individual optical fiber is directly bonded to a film by means of an adhesive or glue.
Japanese Unexamined Patent Publication No. 2001-147330 discloses reinforcing an optical fiber portion from an optical interconnection sheet (optical fiber sheet). The optical fiber was covered with a reinforcing tube and bonded to the sheet by sandwiching the tube between two sheets as shown in FIG. 4. However, the optical fiber portion fixed to the sheet via the reinforcing tube is only a portion of the optical fiber. The remaining larger portion of the optical fiber is directly bonded to the sheet.
The end portion of each optical fiber arranged on the optical interconnection sheet is subsequently connected to an optical connector or the like. Because the optical fiber is directly bonded to the film, if the fiber terminating process fails, the entire optical connection sheet including the other optical fibers will be rendered unusable, decreasing the fabrication yield. Therefore, the end portion of the optical fiber should be provided with an extra length allowing for such failure. Even with the extra length, the situation would be the same if the same failure was repeated.
Another problem may arise when the optical fiber is directly bonded to the film. Transmission loss may occur due to stress concentration at a fiber bend or due to a strain caused by differences in thermal expansion. Expansion arises when the materials expand or shrink due to temperature changes during a temperature test or changes in ambient temperature during use.
Thus, there is a need to provide an optical interconnection sheet that can improve the yield in fiber terminating processing, and can prevent the occurrence of transmission loss due to stress concentration at an optical fiber bend or due to variations in ambient temperature.